This invention relates to barriers, and more particularly to an extension arm for supporting barbed wire at the top of a chain link fence or the like.
To deter would-be intruders from scaling a chain link fence, it is common to top such a fence with a few rows of barbed wire. To make scaling even more difficult, the wire is often supported by arms or extensions which are angled inward or outward, or both, with respect to the plane of the fence.
Prior inventors developed a variety of extension arms for attachment to existing fence posts.
Cox's U.S. Pat. No. 1,773,519 disclosed an arm which could pivot "universally" (actually, only two rotational degrees of freedom were provided) to vary the arm angle.
Subsequently, Miller (U.S. Pat. No. 3,749,368), noting the extreme difficulty work crews have in installing barb arms on fences having top rails, proposed an improvement to facilitate the insertion or replacement of top rails, without disrupting the entire fence. Miller acknowledged Sconzo, U.S. Pat. No. 3,428,300, which disclosed a fence post cap made in two interlocking halves to permit installation about an existing top rail.
U.S. Pat. Nos. 4,603,840, 4,065,103 and 3,771,767 are of additional interest to this invention.
Despite the efforts of prior inventors, installation of barbed wire extension arms to fences remains a difficult task. Additionally, many prior devices can fail or be defeated by applying enough force to them. Some devices, for example, attach to the top rail, which itself may rotate within the post caps.
In both U.S. Pat. Nos. 4,065,103 and 4,603,840, the means of attachment is designed to contact only the fence post. In either case, the limited surface area in contact between the attachment and the existing fence post is detrimental to strength and rigidity. The present invention, in contrast, provides a substantial contact width around the entire periphery of the post.